The present invention relates to a multi-frequency ultrasonic transmitting and receiving equipment having three couples of piezoelectric elements and metal terminals.
In recent years, almost all fishing boats are provided with fish sonars. The fish sonars use various frequencies owing to detecting fishes. When multiple fish boats having the fish sonars of the same frequency are massed in a fishing ground, the fish sonars cannot be executed an original performance owing to crosstalk. Therefore, a fish sonar using multi-frequencies is required.
For solving these problems, fish sonar systems are used which are provided with a plurality of transmitting and receiving equipments operated by various frequencies or transmitting and receiving equipments having a plurality of piezoelectric vibrators operated by various frequencies. Therefore, since the transmitting and receiving equipments become large, these fish sonar systems are unsuitable for a small fishing boat and are expensive.
Also, the other known fish sonar comprises a transmitting and receiving equipment in which the resonance frequencies in the thickness-directional vibration and the diameter-directional vibration of a disk-type piezoelectric vibrator or the thickness-directional vibration, the short side-directional vibration and the long side-directional vibration of a rectangle type piezoelectric vibrator are used. In this fish sonar, however, the length of the diameter of the disk-type piezoelectric vibrator or the length of the one side of the rectangle-type piezoelectric vibrator is limited for input electric power and the directional characteristic of the piezoelectric vibrator. Therefore, in this fish sonar, two or three frequencies separated by long intervals are used.